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May 1, 2012 -- Don't have any motivation at work today? You may be able to blame your brain and its relationship with the chemical dopamine.

The way your brain handles dopamine may predict whether you are a hard worker or a slacker, new research suggests.

"If you look around at the people you know, yourself included, and think of the people always driven to work hard vs. the people who prefer to take it easy, what this study shows is that the range in motivation is in part due to how the dopamine system functions," says researcher Michael Treadway, PhD, a clinical fellow at McLean Hospital and Harvard Medical School.

The new research reflects and reinforces some previous research, Treadway says. The findings could have important implications to help treat conditions marked by decreased motivation, such as depression or attention deficit hyperactivity disorder (ADHD), he tells WebMD.

The study is published in the Journal of Neuroscience.

Dopamine and Motivation

"Our understanding of dopamine has gone through several reiterations," says Treadway. Decades ago, he says, it was known mainly as the ''pleasure chemical."

Experts know, however, that it also plays a role in behavior, voluntary movement, motivation, and reward, among other activities.

In other studies, experts have found that manipulating dopamine has an effect on decisions about working hard for rewards.

Treadway wanted to focus on how the naturally occurring variation in dopamine in people affects their desire to work hard.

With colleagues from Vanderbilt University, he evaluated 25 healthy men and women ages 19 to 29. They spent about 20 minutes in the lab, completing button-pushing tasks.

Some were difficult tasks. Others were easy. For instance, a hard task required pushing a keyboard button 100 times in 21 seconds with a non-dominant pinky finger.

An easy task would be pushing a keyboard button 30 times in seven seconds, using a dominant index finger, Treadway says.

The rewards varied, from about $1 for easy to over $4 for the hard tasks.

Treadway did brain imaging tests known as positron emission tomography, or PET scans. This allowed him to look at levels of dopamine within different brain areas.

Dopamine and Hard Work: Results

Everyone chose a combination of high-effort and low-effort options.

Those who worked the hardest had higher levels of dopamine in two areas of the brain known to be important in reward and motivation. The areas are the striatum and ventromedial prefrontal cortex.

That finding wasn't a surprise. Another was: Treadway found that those not willing to work hard for the reward had high levels of dopamine in another brain area involved in emotion and risk perception. This area is the insula.

"The folks with relatively more striatal dopamine were focused on the reward," Treadway says. "The folks with more insular dopamine were thinking about how tired their pinky was. They were focused on the costs."

Eventually, the findings could help doctors monitor treatment for those with illnesses that dampen motivation, he says.

For instance, differences in dopamine levels might explain why some people respond better to medications such as ADHD drugs, he says.

Dopamine and Motivation: Perspectives

The new research suggests scientists should look at a greater number of brain networks when studying dopamine, says Brian Knutson, PhD, an associate professor of psychology and neuroscience at Stanford University. He reviewed the findings.

"This may have implications for how drugs that influence dopamine may affect effort," he says of the new research.�

The study shows that the amount of effort a person decides to expend seems to depend on where the dopamine is in the brain, says John Salamone, PhD, a professor of psychology and neuroscience at the University of Connecticut in Storrs.

The study, he says, points out that differences in dopamine location from person to person were linked with various degrees of effort.